Web service composition allows a fast and modular creation of applications by orchestrating several Web services. Such applications are frequently faced to performance and availability problems which may affect the partner Web services or the orchestration process itself. This requires mechanisms for adapting the architecture and the behaviour to this variable context. In this paper, we deal with strong mobility of orchestration processes as a mechanism for adaptation. We provide a solution that relies on checkpoint/rollback mechanisms. It is also based on source code transformation of the orchestration process. We apply our approach on WS-BPEL based orchestration processes. Hence, we establish a set of rules which transform WS-BEPL processes to equivalent mobile ones. When an adaptation is to be performed,the execution of some or all instances of a mobile process will be interrupted, and then they will be migrated to another node. After migration, the interrupted instances will resume starting from the last checkpoint. Experimentation results show the the efficiency of our approach and the low overhead it introduces.